An active matrix light emitting device (further referred to as LED) display comprises an array of pixels. Each pixel comprises a pixel driving circuit and a LED. The pixel driving circuit receives an address select signal or a set of address select signals via select electrode(s), a data signal via a data electrode, and a power supply voltage via a power supply electrode to supply a voltage generating a current through the LED. Usually, the pixels are arranged in a matrix comprising columns and rows. In this matrix arrangement, usually, the pixels are selected row by row via the select electrodes extending in the row direction and the data is supplied to the selected pixels via the data electrodes extending in the column direction. The power supply electrodes may extend in the row direction or in the column direction. The grey level of a pixel is determined by the level of the voltage on the data electrode. It is possible to use more than one select electrode to drive the pixel circuit, for example, to control the duty cycle of the light generation. The LED's are current-driven devices of which the luminance is determined by the current that flows through it.
If a particular one of the select electrodes has a voltage indicating to the associated row of pixel driving circuits that the associated row of LED's should be selected, the associated row of pixel driving circuits are programmed by the data signals to supply respective currents to the LED's of the selected row to generate an amount of light corresponding to the value of the respective data signal received via the data electrodes. When a next row of pixels is selected, the state of the previous row of pixels is frozen.
The power supply electrodes supply the current which is required by the LED's to generate light. Thus, if the power supply electrodes extend in the column direction, the current in a particular power supply electrode depends on the state of the pixels in the associated column. If the power supply electrodes extend in the row direction, the current in a particular power supply electrode depends on the state of the pixels in the associated row. Because the power supply electrode has a resistance and current is flowing through it to the pixels, a voltage drop will occur across it which can result in cross-talk. The power supply voltage supplied to each pixel of the display should at least be sufficient for the pixel driving circuit to supply a voltage to the LED to obtain the required current through it. The power supply which supplies the power supply voltage to the power supply electrodes has to be selected sufficiently high to take care of the largest voltage drop possible across the power supply electrode. Consequently, the power consumption of the display will be, on average, much larger than required. This will especially be a problem for large size displays wherein the power supply electrode is relatively long, has a relatively high resistance, and has to supply a high current due to a large amount of LED's which is associated with the power supply electrode.